Halftone camera



April 25, 1961 A. J. POWERS, JR., ETAL 2,981,625

HALFTONE CAMERA 5 Sheets-Sheet 1 Original Filed June 16. 1953 IN VENTORS AUGUST/N J POWERS,\IR-

ANDREW A- AMA/DER Y r4 TTO/FNfYS B Y %7M, g w

April 25, 1961 Original Filed June 16, 1953 HALFTONE CAMERA A. J.POWERS, JR., ETAL 5,. Sheets-Sheet 3 IN V EN TORS AUGUST/N J POWERS, JR.ANDREW K. ANANDER A TTOANEYS.

Apnl 25, 1961 A. J. POWERS, JR., ETAL 2,931,625

HALFTONE CAMERA Original Filed June 16, 1953 5 Sheets-Sheet 5 97 AINVENTORS OZ 1 UGZ/ST/N J P0WER5,JR. QZL ANDREW A. AMA/05R A TTORNEYS.

United rates HALFTONE CAMERA Augustin J. Powers, J12, Glen Head, andAndrew K. Auander, Glen Cove, N.Y., assignors to Powers Chemco, Inc.,Glen Cove, N.Y., a corporation of New York Continuation of applicationSer. No. 361,998, June 16, 1953. This application May 26, 1958, Ser. N:737,974

4 Claims. (Cl. 96116) The present invention relates to a novel andimproved halftone camera especially suited for the production of bothblack-and-white and color separation halftone negatives.

This application is a continuation of our prior copending applicationSerial No. 361,998, filed June 16, 195 3, now abandoned.

Objects and advantages of the invention will be set forth in parthereinafter and in part will be obvious herefrom, or may be learned bypractice with. the invention, the same being realized and attained bymeans of the instrumcntalities and combinations pointed out in theappended claims.

The invention consists in the novel parts, constructions, arrangements,combinations and improvements herein shown and described.

The accompanying drawings, referred to herein and constituting a parthereof, illustrate one embodiment of the invention, and together withthe description, serve to explain the principles of the invention.

Of the drawings:

Figure 1 is a side elevation, partly broken away, showing a typical andillustrative, fragmentary embodiment of a photo-mechanical camerashowing, somewhat schematically, film feeding and cutting means, filmbacking means and mechanism for positioning same, and a halftone screensupporting device in accordance with the present invention;

Figure 2 is a fragmentary sectional view taken along line 2-2 of Figurel and showing the halftone screen supporting frame with a circularhalftone screen mounted therein;

Figure 3 is a fragmentary sectional view taken along line 33 of Figure 2and showing portions of the halftone screen supporting frame and themethod whereby it is movably mounted within the camera body;

Figure 4 is a fragmentary sectional view taken along line 4-4 of Figure2 and showing portions of the screen supporting frame which areadjustably positionable to accommodate screens of various sizes;

Figure 5 is a fragmentary sectional view, on a larger scale, taken alongline 5-5 of Figure 2 and showing a conventional circular halftone screenand its frame as mounted on the screen supporting frame members;

Figure 6 is a fragmentary sectional view taken along line 6-6 of Figure2 and showing other features of the screen supporting frame members;

Figure 7 is a fragmentary perspective view showing the method ofslidably mounting certain horizontal screen supporting frame members ontheir vertical guides and scale means for judging their positionthereon;

Figure 8 is a fragmentary view similar to Figure 2 but showing arectangular halftone screen mounted in the screen supporting framemembers; and

Figure 9 is a fragmentary sectional view, on a larger scale, taken alongline 9-9 of Figure 8.

The present invention is in many respects an improvement upon a Chemcophotomechanical camera shown and described in the prior patent to F. T.Powers No. 2,282,427, granted May 12, 1942, but in other respects theimprovements are of more general application, and may be applied to awide variety of photomechanical cameras utilizingphotographically-sensitized paper or other forms of film which are fedfrom a relatively long roll of film, the proper and desired length offilm being cut from the supply roll and being moved to ex posureposition where the cut portion is held during exposure.

The present invention has for its object the provision of a novel andimproved photomechanical or photoengraving camera in which means arecombined for accurately mounting variously sized halftone screens ofconventional construction in precise parallelism with the filmsupporting plane of the film backing member and maintaining thisparallelism, once it is so adjusted, during movement of the screen awayfrom and to its proper focusing position. The invention further providesa novel and improved combination in which either rectangular halftonescreens or frame mounted, rotatable, circular halftone screens, ofconventional construction, may be used and, in the case of the framemounted circular screen, the screen may be rotated without losing itsparallelism with the film backing member. A further object is theprovision of means on the outside of the camera for moving the adjustedhalftone screen into and out of its focusing or screen separationposition, locking it in any desired position and determining itsposition accurately by a graduated scale associated with the movingmeans.

in general, the camera comprises the usual lens, bellows and film supplyand suction back or film supporting means, all enclosed, as is usual, ina light-tight housing so that extraneous light is excluded. The backingmemher is preferably a suction type of standard construction whichsecurely holds the flexible sheet of film against its lens-facingsurface after the film has been cut from the supply and properlypositioned in front of the backing member. The backing member is movablebodily to wards and away from the exposure plane of the camera and canbe locked in either the rearward film receiving position, or the forwardfocal plane position.

A movable halftoue screen supporting frame is provided which is capableof holding either a rectangular screen or a screen frame with arotatable, circular screen, and is further capable of being adjusted toaccommodate screens of various sizes or diameters. The screen supportingframe is constructed in the form of a large rectangle haviug verticalside members which are held in spaced relation by upper and lowerhorizontal members secured thereto. Secondary vertical bars are providedwhich are parallel and closely adjacent to the vertical members of themain framework and rigidly secured, at their sides, to the horizontalmembers of said framework. Upper and lower cross bars are slidablymounted on the vertical secondary bars and provided at each end with achain mechanism which serves to maintain each cross bar parallel withthe other during any sliding adjustment along the vertical secondarybars.

The upper and lower cross bars serve for the direct support of thehalftone screen and are provided on their rear face, or that facenearest the film backing member, with a plurality of thin aligningplates against which the rear surface of a halftone screen can bepressed. Each cross bar is provided on its front face with a screenframe holding member Which is slidably mounted on studs carried by thecross bars and spring urged towards the cross bars. The upper and lowerscreen frame holding members are adapted to receive the flange of aconventionalcircular screen frame and are provided with a plurality ofclamp screws which serve to secure the flange on the slidable holdingmembers, which being spring urged towards the cross bars, thus press therear face of the circular screen against the thin aligning platescarried by the cross bars. The halftone screen is thus held in exactparallelism with the cross bars regardless of whether the screen is inexact parallelism with its frame or not.

Provision is also made on the cross bars for holding and clamping inplace against the aforementioned thin aligning plates a rectangularhalftone screen which, in conventional practice, is not provided with aframe. A plurality of holding lugs are secured on the front face of thelower cross bar and have their rear faces beveled so that, inconjunction with the aligning plates, a V-shaped trough is formed forreceiving the lower edge of a rec- 'tangular screen. The upper margin ofthe screen is held against the aligning plates on the upper cross bar bya pair of swingable spring fingers pivoted on said upper cross bar. Thusa rectangular halftone screen is held in exact parallelism with thecross bars.

The halftone screen supporting frame as a whole is mounted within thecamera body to have an externally controlled horizontal movement forplacing the halftone screen in any desired position. The supportingframe is hung on horizontal tracks, secured to the camera bodystructure, by means of rollers attached to upper extensions of thevertical side members of the supporting frame. Movement of the frame iseffected by an interconnected rack and gear arrangement providedadjacent each corner of the supporting frame wherein the gears aremounted on shafts which are journalled in bearings secured to the camerabody structure and the racks are secured to the screen supporting frame.Of the four racks provided, one is fixed to the supporting frame whilethe other three are secured thereto by a spring and screw arrangement.The upper gear shaft extends to the outside of the camera body and isprovided at its external end with a crank arm whose distal endcooperates with an arcuate clamping plate on which a graduated scale isprovided. By rotating the crank arm the four interconnected gears arerotated a corresponding amount and hence, through their associatedracks, produce a horizontal movement of the screen supporting frame. Theposition of the frame is accurately indicated by the position of thecrank arm in relation to the scale markings on the clamping plate.

The location and proportions of the mechanism are such that when thecrank arm is rotated clockwise, at least one of the thin aligning plateswill come in direct contact with the front surface of the film backingmember when the latter is in its focal plane position. Adjustment maythen be made, if necessary, to bring all of the aligning plates intocontact with the film backing mem ber by appropriate manipulation of thespring and screw arrangement provided on three of the four racks. Withthe aligning plates in contact with the backingmember and the halftonescreen in contact with the aligning plates parallelism between thebacking member and the halftone screen is assured, fixed and maintainedeven after the backing member and screen are moved away from each otherduring operation of the camera.

It will be understood that the foregoing general description and thefollowing detailed description as well are exemplary and explanatory ofthe invention but are not restrictive thereof.

Referring now in detail to the present preferred and illustratedembodiment of the present invention as shown in the accompanyingdrawings, the invention is shown as embodied in a photo-engraving camerawhich substantially corresponds in its principal parts to a Chemcocamera, many of the parts of which will not be described as they do notrelate to, nor assist in the understanding of the present invention.

The illustrated camera includes the camera body 10, on the forwardportion of which are supported the camera bellows l2, and at the extremeforward portion of which is supported the camera lens 14 which may bemoved back and forth to proper exposure position so that the image to bephotographed is properly focused on the sensitized material. Within thecamera body 10 is supported one or more film supply units, such as thefilm roll 16 from which the deisred length of photographicallysensitized film or paper may be fed to be severed by conventional knifemechanism 13, actuated by external lever 19, so that the desired size ofsheet film may be supported on the forward face of a backing member 20-in a position normal to the axis of the camera lens 14. Between theforward surface of the backing member 20 and the camera lens there isprovided a halftone screen supporting frame 21 in which is mounted thehalftone screen 22. In Figures 1 through 7 halftone screen 22 is shownas a conventional circular screen which is rotatably mounted on a frame23 having a generally rectangular outline. In Figures 8 and 9 aconventional, unframed, rectangular halftone screen 22' is shown mountedin supporting frame 21. The camera body and bellows are so constructed,as is usual, that the film to be exposed is shielded from extraneouslight and receives only that light which is admitted through the shutterassociated with the camera lens 14.

The film backing member 20- preferably is of the vacuum type which isrelatively rigid and provided with a foraminated surface towards thelens by which suction may be applied to a sheet of sensized film to holdit flat and accurately in the focal plane of the camera. At the rear thevacuum backing member 20 is provided with a suction hose 24 which isconnected to a suction pump of suflicient capacity to develop a suctionof several inches of mercury over the entire front surface of thebacking member.

Backing member 29 is also mounted to be moved forwardly and rearwardlywith respect to the focal plane of the camera lens, always maintainingits front surface normal to the axis of the lens, and is preferablymounted so that this movement may be controlled from an exteriormanipulative handle, such as the crank arm 26 which moves over a trackmember 28 to give an external indication of the position of the backingmember with reference to the focal plane, and may also be provided withconventional means for locking the crank arm 26 in its adjusted positionfor exposure. The backing member is conveniently mounted for thisforward and rearward movement by means of the depending legs 30 providedwith rollers 32 which run in horizontally extending tracks 34 fixed toany adjacent part of the camera body structure. The backing member ismoved by means of the parallel link motion parts comprising the links 36which are pivoted on the top and bottom of the backing memher and ateither side thereof and have their rear ends pivoted to rotatablymounted segments 38. Segments 38 are linked together for simultaneousequal movement by means of a pivotally attached vertical link 40.Segments 38 are rotatably mounted by means of shafts which extend acrossthe camera and are supported in the sides of the camera body. The upperones of the segments 38 are rigidly fixed to the shaft on the externalend of which is secured the crank arm 26 so as to be moved thereby, thusmoving all four of the segments 38 and causing a uniform movement of thebacking member 20.

The halftone screen supporting frame 21 is a relatively large,rectangular, slightly resilient framework consisting of verticallyextending side members 46 and 48 connected together near their top andbottom ends and in widely spaced parallel relation by horizontal members55') and 52. The top end of each side member 46 and 48 is provided witha laterally extending roller 54 adapted to roll in a trackway 55 whichmay be secured to the camera body structure 10. Adjacent to and parallelwith the side members 46 and 48 there is provided a pair of secondaryside bars 56 and 58 the ends of which are rigidly secured on thehorizontal frame members 50 and 52. Side bars 56 and 58 may beconveniently formed from strap shaped material and arranged so thattheir broad surfaces face each other. An upper, screen sup porting crossbar 60 and a lower screen supporting cross bar 62 are slidably connectedat their ends to secondary side bars 56 and 58. Each of the fourslidable connections is similar to the others but, as constructed, isformed as right or left hand as its position may require. The left handslidable connection between the upper cross bar 60 and the secondaryside bar 56 as shown in Figure 2, is illustrated in detail in Figure 7.As embodied the side bars 56 and 58 are each provided with inwardlyprojecting lip portions 64 behind which the ends of cross, bars 60 and62 extend. The base of an angle bracket 65 is secured on the forwardface of each bar 60 and 62 near the ends thereof but is spaced therefromby a plate 66 so as to provide a recess into which the lip 64 projects.The flanges 67 of angle brackets 65 lie against the broad inner face ofits associate secondary side bars 56, 58 and are each provided with ahole 68 through which the threaded shank of a clamp screw 69 (Figure 2)extends. A series of threaded holes 70 provided in the secondary sidebars 56, 58 and holes 68 permit each cross bar 60, 62 to be clamped inwith one of the holes 70. Thus, cross bars 60 and 62, which directlysupport the halftone screen 22 or 22', may be moved relative to eachother so as to accommodate screens of various sizes and to center thescreen with respect to the focal axis of the camera lens.

Means are provided to insure that during adjusting movement of the crossbars 66 and 62 each end of a bar moves the same distance no matter wherethe operator may grasp the bar. As embodied such means comprise a crossshaft 72 which is journalled at one end in the secondary side bar 56 andat the other end in secondary side bar 58. This shaft is positionedsomewhat above the uppermost position to which cross bar 66 may be set.A sprocket '73 is fixed on each end of shaft 72 against the inside faceof the adjacent secondary bar. In vertical alignment with each sprocket73 there is an idler sprocket 74 which is located somewhat below thelowermost position to which cross bar 60 may be set and each sprocket 74is rotatably mounted on a stud 75 carried by the secondary sidebar 56 or58. Trained snugly around each pair of sprockets 73, 74 is a sprocketchain '76 and the rear reach of each chain is anchored, as by screws76', to the base leg of its respective angle bracket 65. Thus, movementof one end of cross bar 60 is imparted equally to the other end throughchain 76, sprocket 73 and shaft 72.

A similar movement-equalizing arrangement of sprockets and chains isprovided for the lower cross bar 62 and comprises shaft 77, sprockets 78and 79, studs 80 and chains 81, but shaft 77 and idler sprockets 79 arelocated below and above the cross bar 62, respectively.

Means are provided for easily selecting the proper position of eithercross bar 60 or 62 for holding a halftone screen of a particular size.As embodied, each of the four angle brackets 65 is provided with apointer 85 which is secured on the flange 67 of the bracket at a pointadjacent the hole 68. A graduated scale 86 is provided for each pointer85 and mounted on the outer side of each secondary side bar 56 and 58 ina position corresponding to that occupied by each of the four series ofthreaded holes 7t) in said side bars. Numbered graduations on the scales86 indicate to an operator the level at which cross bars 60 and 62 areto be set to accommodate a particular size screen and when the pointers85 are brought to the desired point the clamp screws 69 are insertedthrough bracket holes 6% into a threaded hole 76 to lock the cross barsin the selected position.

Both upper and lower cross bars 60 and 62 are provided with clamping andaligning devices to accommodate either a conventional, unframed,rectangular halftone screen or a conventional, frame supported,rotatable,

circular halftone screen. In Figures 1 to 7 of the drawings the use of aframed, circular screen is shown and will now be described.

The conventional circular screen 22 is usually held in a rigidlyconstructed frame 23 which is generally rectangular in shape andprovided with grooved rollers 91 at the corners for rotatably supportingthe screen. The screen itself is mounted on the rearward face of theframe 23 and hence the screens back face extends rearwardly of the framea distance equivalent to its thickness and it is this feature which isutilized by the present invention for accurately aligning the planarsurfaces of the screen in parallelism "with the plane occupied by thescreen supporting frame 21.

Referring now to the lower cross bar 62, a screen frame holding member95 is s-lidably mounted thereon by means of a pair of studs 96 (seeFigure 6) which are fixed in the cross bar and project forwardly throughsuitable apertures in holding member and thence termimate in a reducedand threaded end on which a hand nut 97 is screwed. A spring 98, betweenthe hand nut 97 and the forward face of the holding member 95 serves tourge the latter rearwardly towards the cross bar 62. The upper edge ofholding member 95 is formed as a stop to receive and support the loweredge of screen frame 23 and the latter is held in this stop by aplurality of spaced clamp screws 99 carried in plates 100 which arefixed on the front face of holding member 95. Welded, or otherwisesecured to the rear face of cross bar 62 are a plurality of relativelythin aligning plates 101 which project above the top edge of cross bar62 a sufiicient distance so that at least two or more of the plates 161are in the path of the marginal periphery of the rear face of thehalftone screen 22 as the latter is urged rearwardly by springs 98.

Since the weight of the hal-ftone screen and its frame is carried by theholding member 95 the strain on its supporting studs 96 may be relievedby rollers 162 one of which is rotatably mounted in a transverse slotnear each end of the holding member 95. Rollers 102 are adapted to rollon a ledge 103 which may be for-med as part of the lower edge of crossbar 62. Ledge 103 also serves to add rigidity to cross bar 62.

Upper cross bar 60 is provided with a slidably mounted, screen frameholding member 104 carried by studs 105 which are fixed in cross bar6i), extend through suitable apertures in holdingmember 104 andterminate in reduced and threaded shanks on which are screwed hand nuts106. A coiled spring 107 is placed about each stud shank and has one endbearing against the hand nut 106 and the other end against the holdingmember 104 thus urging the latter towards the cross bar 66. A verticallydepending lip 108, formed along the lower edge of holding member 104 andin vertical alignment with the riser of stepped recess formed ontheupper edge of lower cross bar 62, provides a surface against which therear upper margin of screen frame 23 can be clamped. Clamping meanscomprise a pair of fingers 109 which are pivotally attached to theholding member 104, in spaced relation, by knurled hand screws 110. Thedistal end of each finger 199' is provided with a thumb screw 111,which, when the finger is vertically disposed, can serve to clamp thescreen frame 23 against the lip 138 on holding member 104. A ledge 112,formed along the top edge of cross bar 60, provides rigidity to thecross bar and an undersurface of a guide for the holding member 104. Aplurality of relatively thin aligning plates 113 are welded or otherwisesecured to the rear face of cross bar 60 and project below the loweredge of the bar a sutficient distance so that at least two or more ofthe plates 113 are in the path of the marginal periphery of the rearface of the halftone screen 22 as the latter is urged rearwardly bysprings 107. The plates 113 cor- 101 on the lower cross bar 62.

The mounting of screen 22 and its frame 23 is accomplished by firstpartially unscrewing clamp screws 99, associated with the lower crossbar 62, loosening hand screws 110 and thumb screws 111 which are mountedin fingers 109, associated with the upper cross bar 6i), and thenswinging the fingers 1119 to a horizontal position. The lower edge ofscreen frame 23 is then canted into position on the stop provided on theupper edge of holding member 95 and the frame and screen then swung intoa vertical position. The screen is then pressed rearwardly until itrests against the upper and lower aligning plates 113 and 191 afterwhich the fingers 16 9 are dropped to their vertical position andclamped by screws 110. Thumb screws 111 and clamp screws 99 are thenmanipulated so that as their ends press against the screen frame 23 theupper and lower holding members 194 and 95 are forced away from thecross bars, against the urging of springs 107 and 98, until the lip 103on the upper cross bar 60 and the riser of the stop on the lower crossbar 62 are clamped against the rearwardface of the screen frame 23.Thus, the screen 22 is firmly pressed against the aligning plates 101and 113 and thereby held in accurate parallelism wtih the plane occupiedby the screen supporting frame 21 as a whole.

Movement of the halftone screen supporting frame 21 between its forward,or screen loading position, and its rearward, or screen focusingposition, is accomplished by means of a gear and rack arrangement whichis interconnected so =as to produce a parallel motion of the supportingframe 21. As embodied, a pair of upper gears 12% are provided and fixedon a shaft 121 which is journailed in the camera body structure, onegear being to the rear and in line with the upper portion of frame sidemember 46 and the other similarly arranged with respect to frame sidemember 48. A pair of lower gears 122, rotatably mounted on a cross shaft123, are in vertical alignment with upper gears 129' and to the rear ofthe lower portions of side members 46 and 48. Each upper gear 120 isconnected to its corresponding lower gear 122 by a link 124. Thus, anyrotation of upper shaft 121 imparts a corresponding rotation to all fourof the gears. Attached near each corner of the screen supporting frame21 and projecting rearwardly therefrom there is provided a rack 125which is adapted to mesh with one of the gears 120 or 122, and toeliminate lost motion between the gear and rack a pressure roller 126 isrotatably mounted on an adjustable bracket 127 which may be attached toa convenient portion of the camera body structure by belt and slotconnections 128. A jack screw 129 beneath each of the brackets 128provides means for the accurate positioning of the rollers 126.

Of the four racks 125 three are adjustably attached to the framesidemembers 46, 48 while the fourth, shown as the one at the upper leftcorner of the frame 21 in Figure 2, is fixed to the side member 46 as bynut 130. The adjustable connections each comprise a reduced shankportion 131, on the racks 125, which projects through an aperture in theside members and has a hand not 132 screwed on its threaded end.Interposed between the frame side members and the body portion of therack is a compression spring 133. Manipulation of hand nuts 132 thuspermits the screen supporting frame 21 as a whole to be adjusted intoparallelism with a reference plane such as the lens-facing surface ofthe film backing member 20.

Provision is made on the outside of the camera body for moving thescreen supporting frame 21 into a desired position by extending one endof the upper shaft 121, on which gears 12% are fixed,.through a sidewall of the camera body and clamping thereon a hand lever 1 12 which isprovided at its extremity with a locking screw 143. Screw 143 cooperateswith a slot 144- in an arcuate plate 145 which is secured to the camerabody. Graduations 146 on arcuate plate 1.4- provide means for settingthe hand lever 142 in such position as to obtain a particularly desiredposition of the screen supporting frame 21.

. Referring now to Figures 8 and 9 the means for supporting aconventional, unframed, rectangular screen 22' will be described. Aplurality of holding lugs 136 are fixed at spaced intervals along theupper front margin and edge of the lower cross bar 62. That portion ofthe lugs 136 which projects above cross bar 62 has its rear face sharplybeveled so that in conjunction with the adjacent aligning plate 191there is formed a V-shaped trough in which the lower edge of a halftonescreen 22 may rest with the bevel forcing the rear lower margin of thescreen 22' into contact with aligning plate 101. The upper cross bar '60is so adjusted that it is above the upper edge of screen 22 but still insuch position that the rear upper margin of screen 22 may be laidagainst two or more of the aligning plates 113. Spring fingers 137 arepivotally attached to the front face of cross bar 69, as by a screw 138,and provided at their distal end with a screen contacting stud 139 andknob 140. Thus, when the screen 22' is brought against the aligningplates 113 the pivoted fingers 137 may be swung from their horizontal,non-use position in which they are placed during use of a circularscreen, to a vertical position to press the screen 22 against thealigning plates.

Adjustments and operation A halftone screen 22 or 22 of the proper sizeand mesh for a particular photographing operation having been selectedand brought to camera site, the bellows 12 is detached from the camerabody and moved away a sufficient distance to permit an operator to havecomplete access to the interior front of the camera body. The operatinghand lever 142 is then swung to its upper position and locked by clampscrew 143 thereby moving the screen supporting frame 21 to its forwardor screen loading position as shown in solid lines in Figure 1. Upperand lower cross bars 60 and 62 are then moved to the correct positions,as indicated by their pointers and graduated scales 86, so as toproperly receive and center the selected halftone screen, and clamped insuch position by screws 69. Assuming a circular screen is to be used,the lower edge of the screen frame 23 is centrally placed on the lowerholding member and swung to a vertical position, thus bringing the rearupper and lower margins of the screen against aligning plates 101 and113. The screen frame is then clamped into position by upper and lowerclamp screws 111 and 99.

At this point the film backing member 20 is moved to its focal planeposition by manipulating lever 26. This position is indicated in dot anddash lines in Figure 1. Hand lever 142 is now rotated clockwise to movethe screen supporting frame 21 rearwardly until some one of the aligningplates 101 or 113 come to rest against forward surface of the filmbacking member. This will happen if the supporting frame 21 is not inaccurate parallelism with the backing member. By inspection the operatorthen determines which of the aligning plates are not in contact with thebacking member and by manipulation of one or more of the three hand nuts132, which are associated with the adjustable racks 125, shifts thescreen supporting frame 21 until all the aligning plates are in contactwith the backing member. Since the screen is already in contact with thealigning plates and the plates are in contact with the backing memberthe parallelism between screen and backing member is substantiallyperfect. The operator then loosens the conventional clamping meansbetween the hand lever 142 and the shaft 121 and sets and clamps thehand lever at the graduation on the arcuate plate 145. The graduationsof scale 145 indicate varying distances of screen separation from thebacking member, allowance being made in the graduations for thethickness of the aligning plates which is less than the minimum screenseparation required for the photoengraving work to be performed by acamera of the type described herein.

If desired the screen 22 may now be rotated to any position which thework involved requires without destroying the parallelism between it andthe backing member. Since the screen is in contact at all times with thealigning plates any variations in the parallelism between the screen 22and its frame 23 are taken up, during rotation of the screen, by theholding members 104 and 95 shifting their positions on their supportingstuds.

The bellows may now be rejoined to the camera body and conventionalpractice followed in unrolling a strip of sensitized material or film,cutting it to the required size, securing it in place on the backingmember by suction means, moving the backing member from film receivingposition to exposure position, setting the screen supporting frame bymeans of hand lever 142 and graduations 146 so as to obtain the properscreen separation and, finally, completing the operation by exposing thefilm.

The invention in its broader aspects is not limited to the specificmechanisms shown and described but departure may be made therefromwithin the scope of the accompanying claims without departing from theprinciples of the invention and without sacrificing its chiefadvantages.

We claim:

1. In a halftone camera the combination of a halftone screen having acentral portion and an outer peripheral screen, movable means on theframe for urging the align ing members into engagement with the screen,said screen clamped in position between said aligning members and saidframe, means for moving said planar surface and said aligning membersinto contact, means for angularly orienting said frame to move anyaligning members not in contact with said planar surface into engagementtherewith, said aligning members being constructed and arranged to' eachcontact said planar surface when said screen and said surface areparallel, and means for moving said screen and said planar surface awayfrom each other a pre-determined distance to focus and exposure positionrespectively.

2. The invention as set forth in claim 1 wherein said halftone screencomprises a holder and a circular rotatable halftone screen and whereinthe urging means on the frame comprise rotatable clamping elementsmounted on the face of the frame farthest from the rigid planar surface,said clamping members being movable relatively toward and away from thesupporting frame, moving said aligning members into and out ofengagement with said screen.

3. The invention as defined in claim 1 wherein said movable means onsaid frame is adapted to urge said aligning members into engagement witha rotatable circular halftone screen, and including additional meansadapted to co-act with said aligning members for accommodating anon-rotatable rectangular halftone screen.

4. The invention as defined in claim 1 wherein said edge portion of lessthickness than said central portion movable means includes Springs forresiliently urging Said whereby the face of said central portion lies ina plane extending beyond the plane of said edge portion, a rigid planarsurface for supporting photo-sensitive material in the focal plane ofthe camera, a supporting means for the screen, said supporting meanscomprising a frame defining an opening to accommodate the half tonescreen, a plurality of aligning members fixed to the face of the framenearest the rigid planar surface and extending inwardly of the openingat spaced intervals and directly engaging the face of the centralportion of the halftone aligning members into engagement with saidscreen.

References Cited in the file of this patent UNITED STATES PATENTS851,593 Hatt Apr. 23, 1907 1,187,045 De Bouzek June 13, 1916 1,535,225Hayes et a1. Apr. 28, 1925 2,044,184 Powers June 16, 1936 2,115,233Powers Apr. 26, 1938 2,653,510 Huebner Sept. 29, 1953

1. IN A HALFTONE CAMERA THE COMBINATION OF A HALFTONE SCREEN HAVING ACENTRAL PORTION AND AN OUTER PERIPHERIAL EDGE PORTION OF LESS THICKNESSTHAN SAID CENTRAL PORTION WHEREBY THE FACE OF SAID CENTRAL PORTION LIESIN A PLANE EXTENDING BEYOND THE PLANE OF SAID EDGE PORTION, A RIGIDPLANAR SURFACE FOR SUPPORTING PHOTO-SENSITIVE MATERIAL IN THE FOCALPLANE OF THE CAMERA, A SUPPORTING MEANS FOR THE SCREEN, SAID SUPPORTINGMEANS COMPRISING A FRAME DEFINING AN OPENING TO ACCOMODATE THE HALF TONESCREEN, A PLURALITY OF ALIGNING MEMBERS FIXED TO THE FACE OF THE FRAMENEAREST THE RIGID PLANAR SURFACE AND EXTENDING INWARDLY OF THE OPENINGAT SPACED INTERVALS AND DIRECTLY ENGAGING THE FACE OF THE CENTRALPORTION OF THE HALFTONE